1. Field of the Invention
The present invention relates to an image reading apparatus and an image reading method. For example, the present invention relates to image processing such as copying using a scanner.
2. Description of the Related Art
Most of reading apparatuses such as a scanner for reading a document include members such as a mirror, a lens, and a sensor. The characteristics of these members at a time of reading the document change due to factors such as an external temperature, humidity, an operation time, and heat. Thus, an image quality of original image data to be read thereby changes due to the change of these characteristics.
For example, when these characteristics of a mirror and a lens change, a focus vibration value changes, and an image blur generates. Therefore, reading correction should be performed for every image for securing an optimum image quality even when these optical characteristics of the reading system change.
Conventionally, the image reading correction has been performed with the following procedure. A document with a previously created special chart pattern, on which information needed for image reading correction (e.g., chart data with a line pattern) is printed, is prepared, and a reading unit of an image reading apparatus reads the document. Then, based on image data of the read chart pattern, the image reading apparatus performs correction with respect to a change of the optical characteristic of the image reading apparatus, and performs image reading correction so as to acquire desired image data.
Japanese Patent Application Laid-Open No. 2008-118190 discusses a technique for correcting image data. By the technique, a device such as a color printer outputs a color patch to an output unit, and an image reading apparatus generates a forward conversion table for converting a color of a device color space to a device-independent color, based on the colorimetric results of the output color patch. Then, using the generated forward conversion table, the image reading apparatus corrects read image data.
However, the image reading correction discussed in Japanese Patent Application Laid-Open No. 2008-118190 needs an operation including steps of printing the special pattern data on a paper, positioning the printed paper on a document positioning plate of the image reading apparatus by a user, and reading the special pattern data. Therefore, it takes time and effort for a user for causing the apparatus to read the paper, on which the pattern data is printed, for every image reading correction. Further, it is necessary to prepare various pattern data according to various kinds of correction processing.